U.S. patent number 5,279,559 [Application Number 07/846,329] was granted by the patent office on 1994-01-18 for remote steering system for medical catheter.
This patent grant is currently assigned to AAI Corporation. Invention is credited to Irwin R. Barr.
United States Patent |
5,279,559 |
Barr |
January 18, 1994 |
Remote steering system for medical catheter
Abstract
Methods and apparatus are provided for remotely controlling the
bending of an elongated member by implementing energy responsive
control over a member that is configured from two plastic materials
of differing coefficients of thermal expansion. The disclosed
methods and apparatus are particularly applicable for use in
applications such as surgical catheterization where control of the
member from a position relatively remote from the member is
desired.
Inventors: |
Barr; Irwin R. (Sparks,
MD) |
Assignee: |
AAI Corporation (Cockeysville,
MD)
|
Family
ID: |
25297583 |
Appl.
No.: |
07/846,329 |
Filed: |
March 6, 1992 |
Current U.S.
Class: |
604/95.05 |
Current CPC
Class: |
A61M
25/0158 (20130101) |
Current International
Class: |
A61M
25/01 (20060101); A61M 037/00 () |
Field of
Search: |
;604/95,281,264,280-282
;128/772,657,658 |
References Cited
[Referenced By]
U.S. Patent Documents
Primary Examiner: Rosenbaum; C. Fred
Assistant Examiner: Mendez; Manuel
Attorney, Agent or Firm: Venable, Baetjer, Howard &
Civiletti
Claims
What is claimed is:
1. A thermal energy responsive surgical device insertable into the
body of a patient, the device comprising:
a generally cylindrical flexible member comprising a first
non-metallic material having a coefficient of thermal
expansion;
at least one strip formed from a second non-metallic material, said
strip being bonded to said flexible member, said second
non-metallic material having a coefficient of thermal expansion
greater than that of said first non-metallic material; and
a supply system for supplying thermal energy to said second
non-metallic material strip from a position remote therefrom to
effect expansion of said second non-metallic material strip and a
change in angular configuration of said flexible member.
2. The device according to claim 1, wherein said thermal energy
supply system comprising a resistance heater wire connected to said
strip and a source of electrical energy.
3. The device according to claim 2, wherein said heater wire is
comprised of a nickel metal alloy.
4. The device according to claim 2, wherein said heater wire is
provided with a generally sinusoidal configuration along at least a
portion of its length.
5. The device according to claim 1, wherein said thermal energy
supply system comprises an optical energy source.
6. The device according to claim 5, wherein said thermal energy
supply system comprises at least one optical fiber which extends
from said optical energy source to said second material layer.
7. The device according to claim 6, wherein a darkened exterior
surface is provided along at least a portion of the length of at
least one of said optical fibers.
8. The device according to claim 6, wherein at least two of said
second non-metallic material layers are positioned along said
flexible member, a plurality of optical fibers being provided and
arranged such that at least a single one of said plurality of
optical fibers extends from said optical energy source to each of
said two second non-metallic material layers.
9. The device according to claim 5, wherein said optical energy
source comprises at least one laser energy source.
10. The device according to claim 9, wherein said laser energy
source is operable to emit optical energy having a wavelength in
the range of from about 700 nm to about 900 nm.
11. The device according to claim 1, wherein said flexible member
defines a tubular lumen along at least a portion of its length.
12. The device according in claim 1, wherein said flexible member
comprises a radio-opaque indicator adjacent at least one of said
non-metallic material layers.
13. The device according to claim 1, wherein said flexible member
comprises a plurality of strips formed from said second
non-metallic material positioned therealong.
14. The device according to claim 13, wherein said thermal energy
supply system is operable to independently deliver thermal energy
to at least two of said plurality of strips.
15. The device according to claim 14 wherein at least two of said
plurality of second material strips are positioned laterally
adjacent one another at a common level along said flexible
member.
16. The device according to claim 15 wherein at least three second
material a strips are provided along said flexible member at said
common level thereof, at least two of said second material strips
positioned at said common level being independently controllable by
said thermal energy supply system.
17. The device according to claim 13, wherein said plurality of
strips are arranged to form at least two zones located at different
longitudinal positions along the flexible member.
18. The device according to claim 17 wherein the strips comprising
two of said zones are controllable independently from one
another.
19. The device according to claim 1, wherein said first
non-metallic material comprises a polymerized halogenated
hydrocarbon.
20. The device according to claim 19, wherein said polymerized
halogenated hydrocarbon comprises a polyfluorinated alkylene.
21. The device according to claim 1, wherein said second
non-metallic material comprises a silicone rubber.
22. The device according to claim 1, wherein said second material
is received within at least one groove formed within said first
material layer.
23. The device according to claim 1, further comprising an
expansion control system for progressively controlling expansion of
said strips of second material.
24. The device according to claim 1, wherein the material
comprising said second material exhibits a coefficient of thermal
expansion at least twice that of the material comprising said first
material layer.
25. The device according to claim 1, wherein at least one of said
first and second materials is comprised of a material that is
non-antigenic to mammalian tissue.
26. An energy-responsive bi-plastic switch, comprising:
a first member formed from a first plastic material having a
coefficient of thermal expansion; and
a second member positioned along at least a portion of said first
member and being formed from a second plastic material having a
coefficient of thermal expansion greater than that of said first
plastic material, said second member being responsive to thermal
energy input to effect a change in angular orientation of the
adjacent portion of the first member.
27. The bi-plastic switch according to claim 26, further comprising
a supply system for supplying thermal energy to said second
material member to effect expansion thereof.
28. The bi-plastic switch according to claim 27, wherein said
thermal energy supply system comprises a resistance heater wire
coupled to said second material member.
29. The bi-plastic switch according to claim 27, wherein said
thermal energy supply system comprises an optical energy
source.
30. The bi-plastic switch according to claim 29, wherein at least
one optical fiber is provided to transmit said optical energy from
said optical energy source to said second material member.
31. The bi-plastic switch according to claim 26 wherein at least
two zones of second material members are provided along a surface
of said first material layer at different longitudinal positions
thereof.
32. The bi-plastic switch according to claim 31, further comprising
a control system for independently supplying said thermal energy to
each of said zones.
33. The bi-plastic switch according to claim 32, wherein said
control system is operable to modulate the amount of thermal energy
to be supplied to said second material member comprising at least
one of said zones.
34. The bi-plastic switch according to claim 23, wherein the amount
of thermal energy supplied to said second material member is
modulated by varying electrical current flow to said second
material layer.
35. The bi-plastic switch according to claim 32, wherein the amount
of thermal energy supplied to said second material member is
modulated by varying at least one of the duration and rate of
optical energy pulse generation of pulses conveyed to said second
material member.
36. The bi-plastic switch according to claim 26, wherein said first
material member comprises a polymerized halogenated
hydrocarbon.
37. The bi-plastic switch according to claim 36, wherein said
polymerized halogenated hydrocarbon comprises a polyfluorinated
alkylene.
38. The bi-plastic switch according to claim 26, wherein said
second material member comprises a silicone rubber.
39. The bi-plastic switch according to claim 38, wherein said first
material member comprises a material having a coefficient of
thermal expansion that is up to about 20% as high as that of said
silicone rubber.
40. The bi-plastic switch according to claim 26 wherein said first
and said second material members are comprised of materials that
are non-antigenic to mammalian tissue.
41. The bi-plastic switch according to claim 26, wherein said first
material layer is configured as a generally cylindrical tubular
member which defines a tubular lumen that extends along at least a
portion of the length of the tubular member.
42. The bi-plastic switch according to claim 41, wherein said
second material member is positioned along an exterior surface of
said tubular member.
43. A method for effecting bending of a first member in response to
thermal energy input to a second member positioned adjacent the
first member, comprising the steps of:
forming the first member from a non-metallic flexible material
having a relatively low coefficient of thermal expansion;
forming the second member from a non-metallic flexible material
having a coefficient of thermal expansion that is at least twice
that of said first non-metallic material;
bonding the second member along at least a portion of the first
member; and
receiving thermal energy with said second member to effect
expansion thereof and bending of the first member in a
predetermined direction generally away from said second member.
44. The method according to claim 43 wherein said second member is
secured to said first member by receiving at least a portion of the
second member within at least one groove formed within the first
member.
45. The method according to claim 43, wherein said first and second
non-metallic materials are selected from the family of compounds
that are non-antigenic to mammalian tissue.
46. The method according to claim 43, wherein said first member is
formed from a polytetrafluoroethylene.
47. The method according to claim 43, wherein said second member is
formed from a silicone rubber.
48. The method according to claim 43, wherein said thermal energy
arises from the delivery of electrical energy to a metallic member
associated with said second member.
49. The method according to claim 43, wherein said thermal energy
arises from the delivery of optical energy to said second
member.
50. The method according to claim 49 wherein said optical energy is
in the form of electromagnetic energy having a wavelength of from
about 700 nm to about 900 nm.
51. The method according to claim 49, wherein said optical energy
is passed through at least one optical fiber to said second
member.
52. The method according to claim 51, wherein said optical fiber is
provided with a darkened exterior surface along at least a portion
of its length.
53. The method according to claim 51, wherein said optical fiber is
provided with a metallic coating along at least a portion of its
length.
54. An energy responsive device operable to change directional
orientation along at least a single axis, comprising:
an elongated flexible member comprising a first non-metallic
material having a coefficient of thermal expansion;
a plurality of strips coupled to said flexible member, said strips
being formed from a second, non-metallic material and arranged its
discrete zones along said flexible member, said zones being
longitudinally spaced apart from one another along the length of
said flexible member; and
an energy supply system for imparting thermal energy to a
predetermined one or more strip in at least one of said zones from
a position remote therefrom to effect expansion of said one or more
strips and a change in angular orientation of said flexible
member.
55. The device according to claim 54, wherein said energy supply
system comprises a resistance heater wire connected to at least one
of said strips and an electrical energy source connected to the
wire.
56. The device according to claim 54, wherein said energy supply
system comprises an optical fiber connected to at least one of said
strips and a source of optical energy connected to the fiber.
57. The device according to claim 54, further comprising a control
system connected to said energy supply system that is operable to
direct said energy to at least one of said zones.
Description
BACKGROUND OF THE INVENTION
The present invention relates to a remote steering system that is
primarily intended for use with surgical catheters. However, the
invention may also be employed in connection with medical implants,
switchgear and certain industrial pipeline equipment.
Surgical catheterization provides a desirable and readily
implementable procedure for accomplishing various diagnostic and
therapeutic objectives in a manner which is relatively expedient
and free of trauma to the patient. In typical catheterization
procedures, a blood vessel adjacent to the surface of the skin of a
patient is punctured to provide entry of the catheter into the
blood vessel lumen. Once entry of the blood vessel has been
accomplished, the catheter can be advanced through the patient's
vascular system, typically with the aid of various radiographic
imaging techniques, to a desired internal organ or tissue site.
Advancement of the catheter in this manner typically requires
traversing a variety of angled and curved paths. Since many
conventional catheters have generally cylindrical, flexible tubular
structures, passage of the catheter along the desired angled or
curved paths is accomplished by sliding the catheter over a
guidewire.
Depending on the particular catheterization procedure and the path
along which the catheter is to be advanced, the catheter guidewire
may need to be changed on a number of occasions during the course
of the procedure. Such guidewire changeover can be both time
consuming and inherently risky, as vasculature of various
dimensions must be traversed, possibly giving rise to incidents of
vascular trauma and even rupture. Blood vessel rupture can
radically transform the medical procedure from one of relatively
routine diagnostic study to an emergency invasive surgical
procedure, thus jeopardizing the health and even the life of the
patient. Due to the foregoing difficulties and risks, surgical
catheterization has evolved into a surgical specialty in its own
right.
Previous efforts to produce remotely steered catheters have
focussed on the use of shape memory metal alloys in order to
provide desired curvilinear configurations for the distal ends of
the catheters, so as to avoid altogether the requirement for
guidewires. Examples of catheters employing shape memory metal
alloys are disclosed in U.S. Pat. Nos. 4,994,727 and 4,919,133. As
explained in the background portion of the latter patent, shape
memory alloys are capable of transforming from a first
configuration to a second configuration upon reaching a
predetermined threshold temperature. This transformability
apparently arises as a result of the crystalline structure that is
imposed on the metal as a result of the particular metal annealing
regimen that is employed. However, because shape memory alloys are
generally "dormant" with respect to transformability until their
respective transformation temperatures have been attained,
catheters formed from such materials are generally unsuited for all
but the most simple catheterization procedures. These catheters are
generally transformable only into predetermined specific
configurations rather than the broad range of configurations that
are typically required to advance the catheter to remote internal
sites incident to the performance of more sophisticated diagnostic
and therapeutic procedures. For at least the foregoing reasons,
catheters formed from shape memory alloys have not gained
widespread acceptance for surgical catheterization on human
patients.
SUMMARY OF THE INVENTION
In general, methods and apparatus are disclosed for implementing
energy responsive control over the directional orientation or
configuration of an object in response to thermal input. In one
aspect of the invention, the device includes a generally
cylindrical flexible member such as a catheter tube that is
insertable into a conduit such as a blood vessel of a patient. The
flexible member comprises a first layer that is formed from a
non-metallic plastic material having a known coefficient of thermal
expansion. A layer of a second non-metallic, plastic material
having a coefficient of thermal expansion that is greater than that
of the first layer is bonded in an appropriate manner to the first
layer. A thermal energy supply system supplies thermal energy to
the second layer from a position remote therefrom to effect
expansion of the second layer and a change in angular orientation
of the first layer. The thermal energy supply system can be in the
form of a remote control device that is capable of delivering
electrical or optical energy to the second layer for heating
thereof.
Preferred materials for the first and second layers, which together
form what may be referred to as a "bi-plastic", device, are
selected from the families of PTFE fluorocarbons and silicone
rubbers, respectively. However, other non-metallic materials having
suitable physical and chemical characteristics for a given intended
application, and which have sufficiently dissimilar coefficients of
thermal expansion, can be used. A plurality of second layers can be
positioned along the first layer at a common level thereof and can
be arranged such that at least two of the material layers are
independently controllable (i.e., non-slaved to one another) by the
thermal energy supply means. Alternatively, the plurality of second
layers can be arranged to form at least two discrete zones which
are located at different longitudinal positions along the first
layer. In such an arrangement, each of the zones can be
independently controlled. Radio-opaque indicia can optionally be
provided along at least a portion of the flexible member to
facilitate visualization thereof during the course of radiographic
imaging.
In an alternative aspect of the invention, an energy-responsive
bi-plastic switch is provided that includes a first layer formed
from a plastic material having a particular coefficient of thermal
expansion and a second layer positioned along at least a portion of
the first material layer. The second material layer is formed from
a second material having a coefficient of thermal expansion at
least two orders of magnitude greater than that of the first
material and is responsive to thermal energy input to effect a
change in directional orientation of the adjacent portion of the
first layer. A source of energy can optionally be provided to
supply energy to the second layer for conversion to thermal energy.
Alternatively, the switch can be configured so as to derive thermal
energy from the environment in which it is positioned to effect
expansion of the second layer. Such switch configurational
arrangements include, among others, configuration of the switch as
an implantable for use in the body of a mammal for controlling
mammalian body function in accordance with the magnitude of thermal
energy received by the second layer of the switch. When the switch
is to be used in conjunction with mammalian tissue, it is
preferable to form at least one of the first and second layers from
a material such as silicone rubber and a polymerized halogenated
hydrocarbon, respectively, that is non-antigenic to mammalian
tissue. In further arrangements of this aspect of the invention,
the first layer of the switch can be configured as a generally
cylindrical tubular member that defines a tubular lumen along at
least a portion of its length, and the second layer can be
positioned along an exterior surface of at least a portion of the
tubular member.
The present invention further provides a method for effecting
bending of a first member in response to thermal energy input to a
second member positioned adjacent to the first member. The method
comprises the steps of forming the first member from a non-metallic
flexible material having a relatively low coefficient of thermal
expansion, forming the second member from a non-metallic flexible
material having a coefficient of thermal expansion at least two
orders of magnitude greater than that of the first material,
securing the second member along at least a portion of the first
member, and supplying thermal energy to the second member to effect
expansion thereof and bending of the first member in a
predetermined direction generally away from the second member. At
least one groove can be formed in the first member for receivably
retaining therein at least a portion of the second member. The
thermal energy can arise from optical or electrical energy and can
be provided from an energy source to the second member through a
suitably configured lead. Although a variety of optical energy
wavelengths can be employed, energy having a wavelength from about
750 nm to about 900 nm is preferred for many high coefficient of
thermal expansion materials. A tunable GaAlAs (Gallium Aluminum
Arsenide) laser is the preferred source of optical energy.
BRIEF DESCRIPTION OF THE DRAWINGS
Various other features and advantages of the present invention will
become apparent from a reading of the following detailed
description in conjunction with the accompanying drawings, in
which:
FIG. 1 is a schematic side view of a remotely-controllable catheter
device in accordance with the present invention;
FIG. 2 is an enlarged partially exploded view of the distal end of
the catheter device depicted in FIG. 1, illustrating a directional
reorienting device;
FIGS. 3A and 3B provide an illustrative example of the bending of a
catheter through 90.degree. in accordance with the present
invention;
FIG. 4A is a, cross-sectional view of the distal end of the
catheter device taken along line 4A-4A of FIG. 1, illustrating four
directional reorienting devices;
FIG. 4B is an alternative cross-sectional view of the distal end of
the catheter device;
FIG. 5 is a schematic illustration of an electrical control
arrangement for implementing directional control of the device of
FIG. 1;
FIGS. 6A-6C are schematic views illustrating a series of steps for
controlling the directing of a catheter device in accordance with
the present invention through a vascular structure;
FIG. 7 illustrates a perspective view of an alternative embodiment
of the invention employing optical energy;
FIG. 8 is a partial sectional side view of a portion of the device
depicted in FIG. 7;
FIG. 9 is a sectional view taken along the line 9--9 of FIG. 8;
and
FIG. 10 is a schematic illustration of an optical control
arrangement for implementing control of the device of FIG. 7.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
With reference to the drawings, wherein like reference characters
represent like components throughout the various views, and with
particular reference to FIG. 1, there is depicted a bi-plastic
thermal energy responsive device in the form of a
remotely-controllable catheter device 20 that is particularly
advantageous for use in surgical catheterization procedures. It is
to be appreciated, however, that the thermal energy responsive
device of the present invention has a wide variety of uses and can
be configured in a broad range of forms other than remotely
controllable catheter devices to attain a desired utilization
objective. Such alternative uses can include, for example,
exploration of the interior surfaces of conduits such as machinery
pipelines and internal components that would otherwise not be
possible in the absence of disassembly.
The catheter device 20 generally comprises an elongated cylindrical
catheter 22 and a remote catheter control unit 24 designated within
the confines of the box depicted in phantom. The catheter 22
comprises a catheter tube 26 that is dimensioned to be received
within the lumina of major blood vessels such as the saphenous
vein. Preferably, the catheter tube 26 is formed from a
non-metallic, plastic, chemically and hermetically stable material
such as any one of the family of polymerized halogenated
hydrocarbons which include the polytetrafluoroethylenes (PTFE)
compounds. As used herein, the term "plastic" refers to the family
of synthetic or natural organic, non-metallic materials which are
capable of being shaped when soft and then hardened. The family of
PTFE compounds are also noteworthy for their relatively high degree
of thermal stability, remaining chemically and physically stable
when exposed to temperatures in excess of 400.degree. F.
(222.degree. C.).
The catheter tube 26 defines a tubular lumen 28 through which
material such as a suitable radio-opaque dye or other fluid
material or suitably-dimensioned instrument can be passed. A
catheter tube directional reorienting assembly 30 is provided on
the catheter tube 26 and includes four reorienting devices 31 (only
two of which are shown in FIG. 1). The reorienting devices 31 are
preferably positioned diametrically opposite each other as shown in
FIG. 4A. Depending on the degree of directional control of the
catheter tube 26 desired, more or less reorienting devices 31 may
be employed per assembly 30, and more than one assembly 30 may be
positioned along the length of the tube 26.
With reference to FIG. 2, one of the reorienting devices 31 is
shown mounted to a portion of the catheter tube 26. The reorienting
device 31 comprises a layer 33 of suitable plastic material such as
silicone rubber which exhibits a comparatively greater degree of
response to thermal energy input than does the material comprising
the tube 26. Material selection for the tube 26 and respective
layers 33 can vary in accordance with such factors as the chemical
and thermal characteristic of the intended use environment,
material compatibility, and the like. For example, use in the human
body imposes the requirement that the device not contain materials
that are antigenic to human tissue and fluids. Furthermore,
enhanced device response can be obtained through the use of
materials having more widely disparate coefficients of thermal
expansion than the family of PTFE compounds and silicone
rubber.
Material heating apparatus such as a resistance heater wire 32 is
embedded in the plastic layer 33 of the reorienting device 31 in
order to provide thermal energy input in the form of resistance
heat. The resistance heater wires 32 are preferably formed from a
relatively high resistance metal such as an 80:20 nickel-copper
alloy and are supplied with electrical energy via electrical
conductors 34 which are preferably secured to or embedded in the
catheter tube 26. The opposite ends of the resistance heater wires
32 are connected to a suitable ground wire 36, which is also
secured to the tube 26 in a conventional manner. The respective
conductor and ground wires 34 and 36 pass from the catheter tube 26
to the remote control unit 24.
The remote control unit 24 includes a suitable control input device
such as a joystick controller 40 that is displaceable in the manner
indicated in phantom in FIG. 1. Displacement of the joystick 40 in
either of the positions indicated in phantom effects engagement of
a corresponding one of the respective toggle switch actuators 42a
and 42b. Each of the actuators is respectively coupled to a
conventional toggle switch 44a, 44b. The toggle switches 44a and
44b are of conventional design and include a toggle arm 46 that is
selectively displaceable between contact poles 48a and 48b. As can
be appreciated from reference to the drawing, contact pole 48a
represents a switch "open" position, whereas pole 48b represents a
switch "closed" position. Each of the respective toggle arms 46 is
normally biased so as to orient the switch in an "open" position.
Displacement of the joystick 40 to the left or to the right effects
closing of the corresponding switch 44a, 44b by way of the
associated switch actuator to provide for displacement of the
distal end of the catheter tube 26 in a corresponding direction in
the manner described below.
A pivotably-mounted contact arm 50 coupled to a variable resistor
or potentiometer 52 is received within a recess 54 formed within
the undersurface of the joystick control 40. The recess 54 is
defined by a generally continuously-curved surface that provides
for a pair of opposed, inwardly-extending shoulders 56 which are
positioned in close proximity to the free end 57 of the contact arm
50. A power source 58 such as a battery or AC line current that is
transformed and stepped-down to a suitable DC voltage is coupled
between the conductors 34 and the variable resistor 52 to complete
the electrical circuit. Displacement of the joystick 40 toward
either of the extreme positions depicted in phantom in FIG. 1
effects closing of the corresponding switch 44a or 44b and
displacement of the contact arm 50 in a manner proportional to that
of the joystick in order to effect delivery of an electric current
along the respective one of the conductor wires 34 to the
resistance heater 32 of the selected directional reorienting device
31.
In the preferred embodiment of the invention, the layers 33 of the
reorienting devices 31 are formed from a material having a
coefficient of thermal expansion that is at least approximately
two, and preferably up to ten or more, times greater than the
coefficient for that of the material comprising the catheter tube
26. In the preferred embodiment of the catheter device 20, the
layers 33 of the reorienting devices 31 are formed from a suitable
silicone rubber and the catheter tube is formed from a suitable one
of the family of PTFE compounds. Such an arrangement provides for a
disparity in respective coefficients of thermal expansion of on the
order of twelve, whereby silicone rubber is characterized by a
coefficient of on the order of 670.times.10.sup.-6 in/in/.degree.F.
and the PTFE fluorocarbons are characterized by a coefficient of on
the order of 55.times.10.sup.-6 in/in/.degree.F.
While the foregoing materials have been selected for, among other
reasons, their disparity in coefficients of thermal expansion,
other factors relating to the environment in which the device is to
be used may also necessitate consideration. For example, in
instances where the device is to be exposed to body tissues and
fluids of a mammalian patient, considerations of optimal device
performance, as is obtained from the use of materials exhibiting
widely disparate coefficients of thermal expansion, and the extent
to which the material is non-antigenic to mammalian tissues and
fluids, are of critical importance. It can be readily appreciated
that in instances where a risk of adverse antigenic reaction is
posed by the use of a plastic material having an extremely
favorable coefficient of thermal expansion (i.e., a coefficient
that is extremely high or extremely low), prudence would dictate
the use of another, albeit less thermally, advantageous material.
In a corresponding fashion, in instances where the environment does
not dictate such considerations, materials can be selected which
provide for more optimal thermal performance.
With further reference to FIG. 2, shown is the preferred heater
wire configuration for mounting the heater wire 32 within the layer
33. The heater wire 32 is preferably configured with a generally
sinusoidal form comprised of a plurality of laterally
outwardly-extending and inwardly-extending undulations 64 and 66 so
as to increase the surface area for contact of the wire 32 with the
thermally responsive material comprising the reorienting layers 33.
The arrangement of undulations, 64 and 66 permits the heater wire
32 to be configured sb as to form two heater wire segments 32a and
32b that are positioned adjacent one another and connected by a
common bend 68. Configuration of the heater wire 32 in this manner
permits an increase in heater wire surface area from that which
would be provided by the use of straight wire segments so as to
increase the amount of thermal energy that can be transferred to
the material comprising the reorienting layer 33. Thermal energy
transfer is further facilitated by configuring the heater wire as a
generally flat-sided ribbon of generally polyhedral configuration,
as opposed to a circular or oval configuration. Other heater wire
configurations, such as those involving multiple layering of the
wire within the reorienting layer 33, can be provided in accordance
with the present invention.
It is further envisioned as an aspect of the present invention that
the thermal energy responsive device 20 can be formed as, an
integral, self-contained unit comprised substantially entirely, if
not exclusively, of two plastic materials of widely disparate
coefficients of thermal expansion. For such arrangements of the
present invention, sources of thermal energy such as heater wires
32 embedded in the reorienting layers 33 are not required. This
aspect of the invention would have particular utility for use as an
implantable or embeddable object where it is desirable to obtain
some degree of progressive control arising from deformation of the
device 22 upon exposure to thermal energy received thereby from the
surrounding environment rather than an embedded heater wire. Such
arrangements would have particular applicability for use as
implantable devices in mammalian body structures as well as in
non-medical applications, such as for use in progressively
responsive thermal switchgear.
A practical application of the bi-plastic thermal energy responsive
device 20 of FIG. 1 is illustrated in FIGS. 3A and 3B. These
drawings graphically illustrate the dimensions that may be used to
calculate the necessary increase in temperature for effecting
bending or turning of a 0.024 inch (0.61 mm) diameter PTFE tubular
structure such as a catheter 26 through 90.degree. with a 0.5 inch
(1.27 cm) radius. With reference to the drawings, the following
relationship is applicable for determining the circumference or
length of the catheter tube 26 along a 90.degree. bend: ##EQU1##
where C.sup.90.degree. is the circumference of the catheter tube 26
about a 90.degree. bend (i.e., the circumference of a quarter
circle) and R.sub.1 is the radius of curvature of the bend of the
catheter tube 26 (Both the circumference C.sup.90.degree. and
radius R.sub.1, are measured with respect to the central
longitudinal axis of the catheter tube 26.)
Accordingly, a change in the circumference of the tube 26 is
represented by the following relationship: ##EQU2## where,
.DELTA.C.sup.90.degree. is the change in circumference and .DELTA.R
is the change in the radius of curvature. Such a change in
circumference may be as a result of thermal energy input to the
device 22 either through a heater wire or from the surrounding
environment.
The change in radius of curvature .DELTA.R for the tube 26 may be
determined by the following relationship:
where R.sub.2 is the radius of curvature of the directional
reorienting device 31 as measured to one-half of the thickness of
the device, w is one-half the thickness of the directional
reorienting device 31, and W is one-half the thickness of the
catheter tube 26. Given the following dimensions: ##EQU3## and
solving equation (2) above, ##EQU4##
Based on the above calculation, bending of the device 22 through
90.degree. with a 0.5 inch radius results in a circumference change
of approximately 0.028 in (0.71 mm) . The amount of thermal energy
necessary to be inputted to the device 22 in order to effect the
bend, expressed in the form of a temperature increase (.DELTA.T) in
.degree.F., is obtained from the following relationship: ##EQU5##
where, Co.sub.1 and Co.sub.2 represent the coefficients of thermal
expansion of the materials of the catheter tube 26 and the
directional reorienting device 31, respectively, and
2.pi..DELTA.R/4 represents the measurement of a 90.degree. (i.e.,
one quarter) portion of a circle. For a device 22 as described
above formed from silicone rubber (Co.sub.1) and PTFE fluorocarbons
(Co.sub.2), Co.sub.1 =670.degree.10.sup.-6 in/in/.degree.F. and
Co.sub.2 55/10.sup.-6 in/in/.degree.F. Therefore,
Substituting equations (4) and (6) into equation (5),
Therefore, an increase of about 58.degree. F. (14.5.degree. C.) is
required to be imparted to the device 22 along the length of the
tubular member 24 thereof in order to achieve a 90.degree. bend of
the tube along a 0.5 in radius.
The foregoing illustration clearly demonstrates that configuration
of the catheter tube 26 as a bi-plastic member in accordance with
the teachings of the present invention provides the catheter user
with a degree of catheter control that is unprecedented in the
medical field. The extent of angular deviation or bending of the
catheter tube is directly proportional to the amount of thermal
energy imparted to the directional reorienting devices 31.
Operability of the catheter device 20 described above is to be
clearly contrasted with catheters formed from shape memory metal
alloys, where virtually no change in catheter configuration is
attained until a predetermined elevated catheter temperature has
been reached. Once such a predetermined temperature has been
reached, the shape memory material reverts to its pre-shaped form
and, unlike the catheter device of the present invention, is not
readily controllable between its two extremes of configuration. As
a result, catheters formed from shape memory alloys cannot readily
be used in blood vessels having angular deviations more extreme
than that f or which the shape memory material has been
preconditioned. This limitation in the prior art is to be
contrasted with the catheter device of the present invention which,
by virtue of its temperature proportional manner of response, can
be used in any of a wide variety of blood vessel
configurations.
With reference to FIG. 4A, the arrangement for mounting of the tube
directional reorienting devices 31 to the catheter tube 26 is
shown. The four directional reorienting devices 31 are arranged
into two pairs so as to provide f or directional control of the
catheter tube 26 relative to two mutually perpendicular axes. In
the drawings, the relative dimensions of the directional
reorienting devices 31 and the catheter tube 26 have been
exaggerated for the sake of clarity.
In the mounting arrangement depicted in FIG. 4A, the directional
reorienting devices 31 are positioned along the outer periphery of
the tube 26. As the compounds comprising the family of PTFE
fluorocarbons exhibit very smooth and uniform surface
characteristics when formed into three dimensional objects, it is
desirable to alter these characteristics at the sites where the
directional reorienting devices 31 are to be positioned therealong
in order to facilitate binding of these components to one another.
A preferred form of tube surface modification provides for the
formation of a plurality of channels or grooves 72. The grooves 72
can be formed in any of a variety of conventional processes, such
as by cutting with any of a variety of surf ace cutters, and can be
provided so as to extend generally parallel and/or transverse to
the longitudinal axis of the tube 26. Each groove is flanked by a
ridge 74, and the grooves and ridges cooperate with one another to
provide for a region of surface discontinuity which facilitates
bonding of the material comprising the directional reorienting
means 30 to the tube 26.
While the devices 31 have been depicted as being positioned along
or in communication with an exterior surface of the tube 26,
further alternative arrangements, such as those providing for the
layers along the walls defining the tubular lumina 28 are
contemplated by the present invention. With reference to an
alternate embodiment depicted in FIG. 4B, the directional
reorienting devices 31' may be received within
correspondingly-dimensioned channels 70 formed within the periphery
of the catheter tube 26. The channels 70 can be provided with a
variety of cross-sectional configurations, such as that depicted in
the drawing in which the channel sidewalls 70a and 70b converge
toward one another as they extend from a common base wall 70c. The
exterior surface 71 of the directional reorienting device 31' is
preferably provided with a gently curved configuration which, when
combined with the multi-channeled configuration of the tube 26,
provides for a generally annular cross-sectional tube configuration
which facilitates insertion and passage of the catheter into a
blood vessel.
FIG. 5 illustrates in schematic form the control arrangement for
implementing directional control of a device 20 that is configured
in the manner depicted in FIGS. 4A and 4B to be controllable along
at least two mutually perpendicular axes. The control device 24 is
denoted by the phantom line in the drawing. The depicted
arrangement is applicable for use with a joystick controller, key
pad controller, rotary controller, or any of a variety of other
control input devices. The control unit 24 preferably comprises
first and second variable resistors 78, 80, each of which is
connected to a corresponding drive amplifier 82, 84. As can be
appreciated by persons of ordinary skill in the art, the resistance
exhibited by each of the variable resistors 78, 80 varies in
accordance with the position of the control input device (i.e.,
joystick, etc.) so as to vary the amount of current passed through
the corresponding current limiter 86, 88 for passage ultimately to
the corresponding one or more of the directional reorienting
devices 31.
With reference to control of the directional reorienting devices 31
corresponding to elements 1 and 2, output from current limiter 86
is directed to either of the diodes 90, 92 in accordance with the
voltage polarity that is applied across the resistor 78. Current
passing through the respective one of the diodes 90, 92 is
conducted to a connector receptacle 94 for passage to the
appropriate one of the directional reorienting devices 31
corresponding to elements 1 and 2 through a suitable connector 96
and an associated conductor wire 34 extending therefrom. The flow
of current from the second variable resistor 80 to the
corresponding directional reorienting devices 31 corresponding to
elements 3 and 4 proceeds in a manner analogous to that described
above, with current output from the current limiter 88 being
directed to an appropriate one of the diodes 98, 100 in accordance
with the voltage polarity that is applied across the variable
resistor 80.
It will be appreciated from the foregoing description that user
movement of the joystick or other directional control input device
is translated into an appropriate voltage across one or both of the
variable resistors 78, 80 to provide for the delivery of a current
to effect resistance heating of the heater wire 32 embedded in the
respective one or more of the directional reorienting devices 31,
which in turn effects bending of the catheter tube 26 to a
predetermined extent in a predetermined direction. As directional
input can be imparted to the devices 31 for varying degrees of
movement along the respective mutually perpendicular axes, bending
of the tube 26 in a wide range of angular directions between the
respective axes can be attained. For example, equal input to the
resistors 78 and 80 will result in bending of the tube 26 in a
direction which extends 45.degree. between the mutually
perpendicular axes, whereas unequal input will result in tube
bending from 0.degree. to 90.degree. with respect to the respective
axes of control.
Advancement of the catheter 22 formed in the manner described
hereinabove through an anatomical site such as a vascular structure
106 is depicted in FIGS. 6A-6C. Vascular structures similar to that
depicted in FIGS. 6A-6C can be found, for example, in the celiac
axis in the vicinity of the common hepatic and splenic arteries.
The dimensions of the catheter 22 with respect to the blood vessel
106 have been exaggerated for the sake of clarity. The depicted
catheter includes five discrete zones A-E, each of which is
provided with a direction reorienting assembly 30. The direction
reorienting assemblies 30 are preferably arranged to permit
independent directional control of each zone so as to provide the
user with a precise degree of catheter control as the various zones
of the catheter are advanced through the anatomical structure 106.
A visualization marker 108 can be provided adjacent each of the
zones A-E to assist the user in visualizing the position of each
respective zone as it is advanced through the blood vessel 106. The
markers 108 can be formed from gold or any other suitable material
that renders the marker visible during the course of the
catheterization procedure. Gold is preferred for the marker
material when the catheter is to be used in a radiographic catheter
imaging process due to this element's radio-opacity to x-ray
radiation and its relative non-reactivity with mammalian tissue and
fluids.
With continuing reference to the drawings, the vascular structure
106 comprises a primary vessel segment 106a and branching segments
therefrom 106b and 106c. In order to traverse the curvilinear path
extending f rom vessel segment 106a through 106b, the catheter is
advanced (FIG. 6A) in the direction of the arrow beyond the
branched segments 106b and 106c, and thermal energy is directed in
the manner described above to the directional reorienting devices
for zones A and B in order to effect bending of the catheter tube
22 toward the blood vessel branch 106b. Following bending of the
tube adjacent the respective zones to the desired extent, the tube
22 is retracted (FIG. 6B) toward the entry site to the vessel 106b
so as to traverse the bend extending therebetween. Once the bend
has been traversed, thermal energy is imparted in the manner
described above to each of the zones A and B so as to generally
straighten the section of catheter adjacent to these respective
zones. At about the same time, energy is imparted to zone C so as
to effect bending of the tube at this zone toward the vessel branch
106b (FIG. 6C) in order to facilitate advancement of the catheter
tube 22 into and through the vessel branch 106b. Thermal energy is
imparted to zones D and E in a fashion similar to that described
above with reference to zone C so as to further facilitate
advancement of the portion of the tube adjacent these respective
zones into the vessel branch 106b. It will be appreciated that the
number and placement of zones along the length of the catheter tube
can vary in accordance with such factors as, for example, the
anatomy of the structure to be catheterized, the dimensions and
flexibility of the catheter tube, and user preference.
With reference to FIGS. 7-10, there are depicted details of an
alternative arrangement for a thermal energy responsive device,
designated generally by reference character 201, in which optical
energy rather than electrical energy is utilized to provide the
desired elevation in temperature of the directional reorienting
assemblies 30' incident to effecting bending of the tube 26' to the
desired extent and direction. This optical energy embodiment can be
advantageous for use in environments where the passage of
electrical currents along the length of the tube 26' and associated
field effects are to be avoided.
The materials respectively co sing the tube 26' and direction
reorienting layers 31' of the optical energy aspect of the
invention can be the same as those described above with reference
to FIGS. 1-5. The directional reorienting assemblies 301 as shown
are positioned along the outer surface of the tube 26' so as to
form three discrete zones, designated A' through C'. Both the
number and placement of zones can vary for the same reason noted
above with respect to the aspect of the invention depicted in FIGS.
1-5. The respective reorienting devices 31' comprising each of the
assemblies 301 are arranged in a manner analogous to that depicted
in FIG. 4A so as to provide for bending of the tube 26 along at
least two mutually perpendicular axes. As with the arrangement
depicted in FIGS. 1-5, it is to be appreciated that a greater or
lesser number of directional reorienting devices 31' can be
provided at each zone so as to provide for bending of the tube with
respect to a desired arrangement and number of axes.
Optical energy is delivered to the directional reorienting devices
31' through fiber optic leads 34'. Each of the leads can be
provided with a metallic coating to facilitate internal reflection
and can be provided with a darkened exterior surface to promote
energy absorption from the surrounding use environment. In the
preferred embodiment, a single fiber optic lead 34' extends to each
of the directional reorienting devices 31'. However, other
arrangements, such as those involving coupling of a single fiber
optic lead to the directional reorienting devices 31' of each
assembly 30', can be provided. Each of the leads 34' terminates at
its proximal end at a connector 96' which is adapted to be received
within a connector receptacle 94' associated with the control
device 24'.
While the connector 96' and corresponding connector receptacle 94'
can have any of a wide variety of conventional complementary
designs, use of a threaded connector can be advantageous for
providing positive engagement between the connector 96' and
receptacle 94'. With reference to FIG. 7, the connector 96'
includes an externally threaded collar 110 having threads 112 that
are configured and dimensioned to engage complementary threads 114
provided along the surface of the connector receptacle 94'. The
collar 110 defines a central aperture which receives a base 116
through which the proximal ends of each of the fiber optic leads
34' are received for optical coupling in a conventional manner with
appropriate optical energy output devices (not shown) associated
with the control device 24'. Preferably, the collar 110 and base
116 are displaceably mounted relative to one another so as to
inhibit binding or twisting of the leads 34' extending from the
receptacle.
The control device 24' includes a directional input device such as
a joystick 40 that is configured in an analogous manner to that
described above in connection with the embodiment of the device
depicted in FIGS. 1-5 for controlling energy output from the
control 24' to the catheter 22'. In this aspect of the invention,
optical energy is provided: in the manner described below by a
suitable source of optical energy such as a GaAlAs laser diode or
tunable laser. When the control 24' includes a tunable laser,
appropriate wavelength selector means 120 and associated wavelength
display means 122 can be provided. While the selection of
wavelength can vary in accordance with the composition of the
material to be heated, energy having a wavelength from about 700 nm
to about 900 nm is preferred for supplying optical energy to
directional reorienting means 30' formed from silicone rubber.
With reference to FIGS. 8 and 9, there is depicted the preferred
configuration for the directional reorienting devices 31' for use
in conjunction with the receipt of optical energy. While each block
constituting the devices 31' can be provided with a substantially
uniform and solid cross-sectional configuration, it is preferred
that the block 31' define an open chamber 130 which extends
substantially parallel to the principal axis of the block to allow
for a substantially even distribution of optical energy for
radiation to the material comprising the block 31'. The block
surface 132 defining the chamber 130 is preferably provided with a
smooth, uniform surface to facilitate internal reflection of the
optical energy within the chamber. The distal end 134 of the fiber
optic lead 34' is embedded in the block 31' in such a fashion so as
to preferably extend partially into the chamber 130. It is to be
understood, however, that other mounting arrangements for securing
the lead distal end 134 within the block 31' can be provided.
Furthermore, it is to be appreciated that, while a single lead 34'
is depicted as extending to each of the blocks 31', the depicted
single lead can instead be in the form of a cable comprising a
plurality of discrete fiber optic leads for conveying optical
energy to the blocks 31'. Optical energy transmitted to the blocks
30' in any of the foregoing ways is radiated to the material
comprising the block to cause an elevation in block material
temperature to effect its elongation and, therefore, angular
deviation or bending of the portion of the tube 26' to the desired
extent and direction.
FIG. 10 illustrates in schematic form the circuitry that is
associated with implementing optical energy input to the
directional reorienting devices 31'. The figure provides a
schematic circuit diagram for a single-zone, two-axis range of
directional control and operates in a manner generally analogous to
that described above in connection with FIG. 5. In particular,
first and second variable resistors 78', 80' are provided to vary
the signal input to associated drive amplifiers 82', 84' in
accordance with joystick position. As was the case with the
arrangement depicted in FIG. 5, signal input for controlling
directional input for movement along one axis is depicted in the
upper half of the drawing, whereas signal input for controlling
directional input along a second axis which is perpendicular to the
first axis is depicted in the lower portion of the drawing. As
noted above, control for a different orientation or number of axes
of movement can be provided in accordance with the present
invention. Output from the respective drive amplifiers 82', 84' is
directed in parallel to a corresponding wavelength selector and
pulse time-pair, labelled 121, 123 and 125, 127 in the drawings,
for processing and routing of signal input to appropriate
directional reorienting devices 31' that have been provided for
controlling movement of the catheter tube 26' along the associated
one or more axes of movement. An optical energy pulse is generated
by optical energy source 128 in accordance with signal input
parameters from the wavelength selector and pulse timer pairs that
is commensurate to the quantum of energy that is required to
accomplish the desired extent of deviation along the respective
axis of movement that is inputted to the control 24' through the
joystick 40. As noted previously, the optical energy source 128 is
preferably in the form of a laser diode or tunable laser which is
capable of generating optical energy output of an appropriate
wavelength and pulse duration to the selected directional
reorienting devices 31' through the fiber optic leads 34' in the
manner described above.
The foregoing detailed description is illustrative of various
embodiments of the thermal energy responsive device of the subject
invention. It will be appreciated from the foregoing description
that variations can be made to the invention as set forth
hereinabove and in the accompanying drawings, and such variations
are expressly intended to be encompassed by this description and
the accompanying claims.
* * * * *